1. Field
The present disclosure relates to a drying device for drying ink discharged onto a surface of a recording medium such as a paper sheet. The present disclosure relates also to an ink jet recording apparatus equipped with the drying device, which performs recording on a recording medium such as a paper sheet by discharging ink from a plurality of nozzles.
2. Description of Related Art
Recording apparatuses including a copy machine, a printer, and a facsimile are configured to record images such as characters, graphics, patterns, and so forth on a recording medium such as a piece of paper, a piece of cloth, an OHP sheet, or the like. Recording methods adopted by these types of recording apparatuses can be classified into a dot impact method, a thermal transfer method, an electrophotographic method, an ink jet method, and so forth. Furthermore, these recording methods can be classified further into a serial type and a line head type. The serial type is a technique in which a recording head performs recording while scanning over a recording medium in a direction perpendicular to a conveying direction of the recording medium. The line head type is a technique in which a recording head formed to be relatively elongated in a direction perpendicular to a conveying direction of a recording medium is fixed to an apparatus and performs recording on an entire surface of the recording medium as the recording medium is conveyed.
For example, a line head type ink jet recording apparatus includes a line head having a recording region in a direction perpendicular to a conveying direction of a recording medium such as a paper sheet, namely, a recording region corresponding to the width of the recording medium. The line head type ink jet recording apparatus records, while conveying the recording medium, an image on the recording medium by discharging ink onto a surface of the recording medium from each nozzle of the line head. This allows the line head type ink jet recording apparatus to perform higher-speed recording compared with a serial type ink jet recording apparatus in which a recording head performs scanning in a width direction of a recording medium.
Among such ink jet recording apparatuses is a type equipped with a drying device that dries ink discharged onto a recording medium, which has been disclosed as prior art. An ink jet recording apparatus of this type, which has been disclosed as prior art, includes a drying device having a drying fan that is provided in opposition to an ink recording surface of a recording medium and blows air toward the ink recording surface. That is, by using the drying fan, the drying device blows air from above toward an upper surface of the recording medium onto which ink has been discharged in an attempt to dry the ink.
In order for ink discharged onto a recording medium to be dried as quickly as possible, moisture in the ink needs to evaporate quickly. The simplest method for causing moisture in the ink to evaporate is to blow air toward the ink as the above-described conventional drying device does.
At the time when ink evaporates, a diffusion layer of water vapor that has not reached its saturation water vapor pressure is formed around the ink. The evaporation proceeds as moisture passes outward through the diffusion layer. Increasing the flow velocity of air around the ink allows the water vapor diffusion layer to be formed with a decreased thickness. In this case, since the gradient of a water vapor pressure increases with decreasing thickness of the water vapor diffusion layer, the evaporation of moisture in the ink can be further accelerated.
In a case of causing moisture in ink to evaporate by utilizing an airflow as described above, a drying device should be structured so as to provide an airflow having a highest possible velocity. In the above-described conventional drying device, however, since a blow-off port of the drying fan is provided in opposition to an ink recording surface of a recording medium, an airflow flows to directly strike the ink recording surface. For this reason, an airflow generated by the drying fan is likely to be immediately decelerated, and this deceleration is observed significantly at a position distant from the blow-off port.
Furthermore, in the above-described prior art, an airflow generated by the drying fan directly impinges only on a narrow area immediately below the blow-off port. As a result, a period of time in which an airflow generated by the drying fan directly impinges on a recording medium being conveyed is extremely short. Hence, in a case where a drying device capable of continuous and high-speed processing is desired, the above-described prior art cannot be said to be effective enough to dry ink discharged onto a recording medium as quickly as possible, thus leaving room for improvement.